Hi Z Grant, and welcoe to TW Community!
You need the file back to .php (get a clean 3.0 file set for installation, I would say).
It seems to me that something is needed for the php5 to be available for Tiki (maybe the web server needs to be restarted by the sys admins, if they didn't do so? Or maybe Tiki keeps some files in the temps folders (just a guess)?
But for sure, if you rename files, Tiki won't find them since Tiki expects them to be called as they are *.php .
My 2 cents.